High-Performing Flexible MgBi Thin-Film Thermoelectrics.

With the advances in bulk MgBi, there is increasing interest in pursuing whether MgBi can be fabricated into flexible thin films for wearable electronics to expand the practical applications. However, the development of fabrication processes for flexible MgBi thin films and the effective enhancement of their thermoelectric performance remain underexplored. Here, magnetron sputtering and ex-situ annealing techniques is used to fabricate flexible MgBi thermoelectric thin films with a power factor of up to 1.59 µW cm K at 60 °C, ranking as the top value among all reported n-type MgBi thin films. Extensive characterizations show that ex-situ annealing, and optimized sputtering processes allow precise control over film thickness. These techniques ensure high adhesion of the films to various substrates, resulting in excellent flexibility, with <10% performance degradation after 500 bending cycles with a radius of 5 mm. Furthermore, for the first time, flexible thermoelectric devices are fabricated with both p-type and n-type MgBi legs, which achieve an output power of 0.17 nW and a power density of 1.67 µW cm at a very low temperature difference of 2.5 °C, highlighting the practical application potential of the device.